Miniaturized direct current fan

ABSTRACT

An axial flow fan for ventilating electrical and electronic equipment includes a brushless, DC external rotor-type central drive motor wherein the rotor is covered by a thermally-insulative impeller. The rotor is supported by a bearing tube formed of plastic, integrally moulded with a mounting flange. In one embodiment, the fan casing forms part of the integral plastic molding.

This application is a continuation of application Ser. No. 068,741 filedJune 25, 1987, now abandoned, which is a continuation of Ser. No.634,677 filed July 30, 1984, now abandoned, which is a continuation ofSer. No. 466,960 filed Feb. 16, 1983, now abandoned.

The invention relates to a miniaturized direct current fan, particularlyfor ventilating electrical or electronic equipment.

Numerous miniaturized direct current fans are known and these generallyhave a polygonal contour, usually that of a square in an axial plan viewon the rotor axis. In such a standardized parallelepipedic casing, thereare also standardized mounting holes, quadratically spaced in the cornerarea of the square contour of the casing. Generally, such blowers areconstructed as axial-flow blowers, i.e. the feed direction is parallelto the rotor axis of the drive motor arranged centrally in the casingarea. It is not only the square lateral length of the casing, but alsothe axial length of the square, i.e. the fan casing length in the feeddirection, which is generally standardized.

Such fans, generally called electronic fans and constructed in the formof axial-flow blowers have been used for roughly two decades and areusually operated with alternating current. However, there has of latebeen an increasing demand for direct current operation of such fans.Alternating current drives for such fans are already known in connectionwith very small dimensions, an improvement in efficiency being obtainedby increasing the frequency. There are already direct current drives forvery small fans. However, such known solutions have a disadvantageousservice life, because they are driven with brush motors and external,complicated electronics are required.

The problem of the invention is to provide in connection with a verysmall fan, particularly an axial-flow fan of the aforementioned typewith dimensions of less than 80×80×35 mm, an economically advantageousblower unit for direct current operation which has a very long servicelife, low consumption, a compact overall arrangement (i.e. the completedrive electronics for the fan can be housed in the square area), a highblower efficiency, a good feed characteristic (volume per second undervariable pressure) and a moderate power consumption (preferablyapproximately constant with variable speed).

The smaller the blower, particularly the axial-flow fan, the morenoticeable the advantages in the case of a solution of this type.(However, the arrangement is not limited to axial-flow blowers, becausethe same advantage, at least with respect to the compactness of themotor to be driven and the integration of the motor electronics in themounting flange of the motor can be obtained in the case of a very smalldiameter radial blower). However, the two combination features of motorand such a casing configuration have a particularly advantageous effectin the case of a very small fan, e.g. less than 70×70 mm and with anaxial length of 15 to 30 mm.

Thus such a motor has very reduced electronics which can be economicallyand advantageously housed in the motor flange, particularly in the caseof mass production so that, unlike in the case of known solutions, noexternal electronics are required.

In addition, the casing configuration with such a small fan andparticularly with a ratio of the diameter of the central drive unit tothe impeller diameter of approximately 1:2 (or greater than 0.5) isparticularly advantageous, the latter applying equally to radial andaxial-flow blowers.

Another independent solution is described, in which at leastapproximately the flow duct is shaped like a Venturi tube. Here again,the advantages of the solution according to the invention areparticularly apparent with casing dimensions below 70×70×30 mm.

Embodiments of the invention are described hereinafter relative to thedrawings, wherein show:

FIG. 1 a plan view of the outlet side of the fan according to theinvention.

FIG. 2 the section along line II--II of FIG. 1.

FIG. 3 the section along line II--II of FIG. 1 through a fan accordingto the invention with a different blow duct configuration.

FIG. 4 the circuit diagram of the drive motor.

FIG. 5 another circuit diagram of the drive motor.

FIG. 6 a diagram of the feed characteristic of the fan according to theinvention.

FIG. 7 a modified embodiment with respect to FIG. 2, but also alongsection line VII--VII of FIG. 1.

A fan 1 (FIGS. 1 and 2) comprises a casing 2, whose webs 3 connect saidcasing 2 to a centrally arranged motor 5, via a flange 4. These webs 3are positioned on the outlet side, so that the noise produced by the airmovement is reduced. Casing 2, webs 3 and flange 4 are preferablyconstructed in one piece.

Motor 5 is an external rotor-type motor, which will be described ingreater detail hereinafter. An impeller 6 is fixed (bonded or shrunk-on)to the outer casing of motor 5. Impeller 6 preferably has seven fanblades 7, which are distributed in irregular manner around theperiphery, thereby damping annoying pure tones.

Between the fan blade 7 and the inner wall 8 of casing 2 is formed asubstantially cylindrical flow duct. The external diameter of impeller 6(outer fan blade diameter) is to be only slightly smaller than thediameter of the inner wall 8 of casing 2, in order to optimize the airflow (FIG. 2). Very good results are obtained if casing 2 and impeller6, including its fan blade 7, are produced from glass fibre-reinforcedplastic by the injection moulding process.

The feed capacity of the fan is further increased if, at least one theoutlet side of the flow duct, widening takes place in the contourcorners 9 of casing 2 in such a way the widened or enlarged portions 10extend significantly beyond the diameter of impeller 6, 7. This cornerwidening particularly helps to improve the efficiency in the case offans of this type (base area 62×62 mm, axial length 25 mm). On the inletand/or outlet side of contour corners 9 are also provided mounting holes11.

Ball bearings 12 are used for mounting the rotor of motor 5, whichrotates at a speed of approximately 5000 r.p.m. Cheaper slidingbearings, which are used in the case of larger fans, are not suitablehere, particularly due to the high speeds.

The ball bearings 12 are placed in a bearing tube 18, whose externaldiameter is reduced in the vicinity of the stator laminations, in orderto obtain an adequate iron cross-section for the magnetic circuit thereby means of the slot bottom in the stator, which should be as close aspossible to rotor shaft 19. At one end, bearing tube 18 is fixed byrolling to flange 4, 24, which leads to further space saving. The flowdirection is indicated by arrows 13 and 14.

Similar conditions exist in the case of the embodiment of FIG. 7, but inthis case the bearing tube 99 receiving bearings 12 is additionallyinjection moulded in one piece to flange 4 and surprisingly this has anadequate precision and thermal stability for continuous operation inconjunction with a commutatorless direct current motor operated intwo-pulse manner. The casing, flange, webs and bearing tube form asingle plastic moulding and bearing tube 99 has injection mouldedshoulders 99A, 99B, 99C for the engagement of bearings and stator. Inplace of the aforementioned two-pulse, commutatorless d.c. motor with anauxiliary reluctance moment, which is advantageously constructed inaccordance with U.S. Pat. No. 3,873,897 which is hereby incorporatedinto the present application, it is also possible to operate with atwo-pulse commutatorless d.c. motor without an auxiliary reluctancemoment, e.g. in accordance with U.S. Pat. No. 4,371,817 which is alsoincorporated into the present application. In conjunction with saidmotor, the central bearing tube can also be made from plastic and ismoulded in one piece with the flange, webs and outer casing. However,particular advantages are obtained with a two-pulse, auxiliaryreluctance moment motor, because its efficiency is particularly high(particularly if in accordance with U.S. Pat. No. 3,873,897) and itsheating is correspondingly low, which conversely means a relatively highstability of the bearing tube.

FIG. 3 shows another embodiment according to the invention. A fan 21comprises a casing 22, which has webs 23, which pass over into a flange24, provided centrally with respect to the square base area of casing 22(corresponding to FIG. 1). Casing 22 webs 23 and flange 24 are in onepiece and a motor 25 is fixed to flange 24. An impeller 26 with fanblades 27 are fitted to the outer casing of the motor. In this case, theflow duct 28 is in the form of a Venturi tube and on the outlet side, inaccordance with the embodiment of FIGS. 1 and 2 of flow duct 18,enlargements 30 are provided into the contour corners 29 of casing 22.On the inlet and outlet sides of contour corners 29, there are mountingholes 31 (spacing 50×50 mm).

Motor 5, 25 is a commutatorless d.c. motor for one or two-pulseoperation with a so-called auxiliary reluctance moment, which is broughtabout in that the electrodynamic moment from the stator winding only hasan a.c. field and the magnetic resistance of the magnetic circuit in thestator region is so modified over the rotation position of the impeller,that magnetic energy is stored for as long as the electrodynamic momentdrives in pulsewise manner and in the pulse gaps, the stored magneticenergy is freed again by the cooperation of the rotor permanent magnetswith the stator iron accompanied by torque formation. Such motors aredescribed in detail in DAS 2,225,442 and German Patent 2,346,380 (SwissPatent 597,715). The electronics for controlling such a motor (describedin DOS 3,010,435.9) require fewer components than conventional d.c.motors of this type, so that it is possible to house within the externaldimensions of casing 2, 22 of fan 1, 21 the electronics for commutatingthe motor.

To avoid unnecessary length, reference is made to the aforementionedpublications (DAS 2,225,442, German Patent 2,346,380 and DOS 3,010,435)and particularly to FIGS. 6 and 7 of the latter. Due to lack of-space,the relatively large capacitors 67, 74 (FIG. 6 of DOS 3,010,435) usedfor block securing purposes are omitted and replaced by a PTC-resistor78 in the positive line 33.

FIG. 4 shows such a circuit, in which there is a matching network 65comprising three resistors. From output 50 of Hall-IC's 55, a resistor66 leads to the positive line 33, a resistor 67 to the base of apnp-transistor 69, said base being connected across a bleeder resistor70 to the positive line 33 to which is also applied the emitter oftransistor 69. The Hall IC 55 serving as a rotor position-dependentsensor is connected with one terminal to the negative line 35 and withthe other terminal, across a resistor 48 to the positive lines 33.Parallel thereto is provided a Zener diode 49, which regulates thevoltage at Hall IC 55. In addition, from output 50, a resistor 73 leadsto the base of an npn transistor 75, which is also connected across ableeder resistor 76 to the negative line 35, to which is also appliedthe emitter of said transistor. The collector of transistor 69 isconnected to terminal a1 of winding W1, while the collector oftransistor 75 is connected to terminal a2 of winding W2. The by-passdiodes 59 and 60 are connected in antiparallel to the associatedtransistors 69 or 75. Coupling capacitor 47 is positioned betweenterminals a1 and a2.

lf on starting, a north pole faces Hall IC 55, its output potentialbecomes low and it approximately assumes the potential of negative line35. Thus, a charging current flows across the emitter-base junction oftransistor 69 and makes the latter conductive, so that a current flowsin winding W1. If this current is subsequently switched off, the energyfrom winding W1 is recovered by coupling capacitor 47 and diode 60 viathe transformer coupling. Transistor 75 is then conductively controlled.If the rotor is blocked, the conductive transistor 69 or 75 stillreceives part of the relatively high starting current, but very rapidlyheats the PTC-resistor 78 located at the input, so that its resistancerises sharply in accordance with its characteristic curve andconsequently the actual current in the blocked state is reduced to 10 to20% of the "normal" short-circuit current value. Thus, the currentacting on transistor 69, 75 is so low that they are not thermallyendangered.

The circuit according to FIG. 4 represents an economically advantageoussolution for such a miniaturized fan, because the relatively fewcomponents have to be housed in space-saving manner in the flange of thevery small drive motor, despite fulfilling the requirements of blockingprotection and protection against wrong poles (by means of thePTC-resistor 78 located at the input and which is also housed in thisflange).

A further reduction of the components is achieved with a circuitaccording to FIG. 5. A parallel-wire winding (so-called bifilar winding)makes it possible to use smaller capacitors, while the number ofcapacitors can be reduced. Through the use of the PTC-resistor 78 andthe bifilar windings (W₁ ', W'₂), there is no need for the capacitors45, 47, 68, 74 used in DOS 3,010,435 (FIG. 6).

In place of the simple transistors 69,75 according to FIG. 4, in thiscase complementary Darlington transistors 80, 81 are used and preferablythose types already contained in the bleeder resistors 80', 81' and theby-pass diodes 80", 81". As the Darlington transistors have a muchgreater current amplification than ordinary transistors, they can alsobe controlled with higher impedance RC-elements.

The Hall IC is constituted by a type having integrated voltagestabilization (e.g. UGN 3016 "Sprague"), so that diode 49 (FIG. 4) isrendered superfluous.

The resistance network 82 serving as a matching element can in principlebe constructed here in the same way as network 65 of FIG. 4. Junction 83is connected across a resistor 85 to the positive line 33, across aresistor 86 to the base of transistor 80 and across a resistor 88 to thebase of transistor 81. The arrangement of capacitors 16, 17 between thebases of transistors 80, 81 and lines 33, 35 improves the switchingbehaviour.

The emitter of the pnp-transistor 80 is here again connected to thepositive line 33, its collector is connected to terminal a1 of windingW₁ ', and the emitter of the npn-transistor 81 is connected to thenegative line 35, while its collector is connected to terminal a2 ofwinding strand W₂ '.

FIG. 6 shows the feed characteristic of a fan according to the inventionwith external dimensions 62×62×25 mm and with a speed of 5000/6000r.p.m. for 12/13V d.c.

We claim:
 1. A miniaturized, axially compact fan for ventilatingelectrical and electronic equipment, comprising:a brushless, directcurrent, external rotor-type central drive motor having an inner stator,an outer rotor at least radially surrounding the stator, and acylindrical air gap therebetween, said drive motor not exceeding atwo-pulse operation and including electronics for controlling the motor,said motor having a central rotor shaft journalled in a pair of ballbearings mounted in an axially extending bearing tube which is supportedby a mounting flange, said inner stator being configured to have aninner axially extending surface and said inner stator being mounteddirectly on the bearing tube for a substantially axial length of thatinner surface closely surrounding a corresponding axial length of anouter surface of the bearing tube, at least the mounting flange and thebearing tube being formed together in one integral piece from plastic byinjection molding, and the mounting flange carrying the motorelectronics; an impeller fastened to the outer rotor of said motor; afan casing supporting the mounting flange, said casing being in the formof a parallelepiped surrounding said impeller; and a flow duct formed byan inner wall of said casing around said impeller.
 2. A fan according toclaim 1, wherein said central drive motor includes an outer diameterhaving a ratio of not less than 0.5 to an outer diameter of saidimpeller;the fan casing parallelepiped is no larger than a 70×70 mmsquare with mounting holes located quadratically in the corners of thecasing, the axial length of the casing being between 15 to 30 mm; andthe flow duct formed by the inner wall of said casing around saidimpeller is cylindrical, said outer diameter of said impeller being onlyslightly smaller than that of the inner wall, said flow duct on its airoutput side being widened into the corners of the casing and increasingthe diameter thereat significantly over that of the impeller.
 3. A fanaccording to claim 2, wherein the base area of said casing is 62×62 mmand the axial length of the fan is 25 mm.
 4. A fan according to claim 2,wherein the drive motor is for two-pulse operation with a magneticresistance of the stator being variable over a rotation angle whichproduces an auxiliary reluctance moment, and being staggered in timewith respect to an electrodynamic torque produced by the motor.
 5. A fanaccording to claim 2, wherein the fan casing surrounding the impeller isinjected moulded in one piece on the flange, so that the casing, flangeand bearing tube form a single plastic part.
 6. A fan according to claim2 wherein the motor electronics includes only two transistors and onerotor position sensor.
 7. A fan according to claim 2 wherein the motorelectronics includes a PTC resistor in one input line between thevoltage and all other electronic components.
 8. A fan according to claim7 wherein the stator includes only two winding coils which areconstructed as bifilar windings.
 9. A fan according to claim 1,whereinsaid central drive motor includes an outer diameter having aratio of not less than 0.5 to an outer diameter of said impeller; thefan casing, in axial plan view, concentrically surrounds said impellerwith a radial symmetrical contour and is no larger than a 70×70 mmsquare with mounting holes located quadratically in the corners of thecasing, the axial length of the casing being between 15 to 30 mm; andthe passage cross section of the flow duct at first decreases in thedirection of air flow to a minimum in the manner of a Venturi tube andthereafter said flow duct on its output side is widened into the cornersof the casing and increases the diameter of its cross section thereatsignificantly over the minimum, the radical outer edges of the impellermostly conforming to the shape of the casing inner wall.
 10. A fanaccording to claim 9, wherein the base area of said casing is 62×62 mmand the axial length of the fan is 25 mm.
 11. A fan according to claim9, wherein the drive motor is two-pulse operation with a magneticresistance of the stator being variable over a rotation angle whichproduces an auxiliary reluctance moment, being staggered in time withrespect to an electrodynamic torque produced by the motor.
 12. A fanaccording to claim 9, wherein the fan casing surrounding the impeller isinjected moulded in one piece of the flange, so that the casing, flangeand bearing tube form a single plastic part.
 13. A fan according toclaim 9 wherein the motor electronics includes only two transistors andone rotor position sensor.
 14. A fan according to claim 9 wherein themotor electronics includes a PTC resistor in one input line between thevoltage source and all other electronic components.
 15. A fan accordingto claim 14 wherein the stator includes only two winding coils which areconstructed as bifilar windings.